Re: [Bug-gdb] GDB and X11 server grabs
On Sep 18, 11:46am, Pierre Sarrazin wrote: > Dixit Kevin Buettner (2000-09-14 16:34): > > Also, it's possible to run commands in the shell via the `shell' > > command, so the original poster (Pierre) could put something like the > > following in his .gdbinit file: > > > > define hook-stop > > shell clear_xgrab > > end > > > > Provided that a suitable external program called `clear_xgrab' was > > created, this would do what the original posted wanted. > > I wrote a program that calls XUngrabServer(), but it did not have > any effect. I added a call to XGrabServer() juste before, but still > without effect. Perhaps a server grab is specific to each X11 client. > Ungrabbing from one X11 client would not affect grabs by other clients. Perhaps you need to use XUngrabPointer() ? > I wouldn't mind patching my own copy of GDB to experiment > with XUngrabServer(). Could someone tell me what function > of the GDB sources I should study to do this? I would like > to add some code where GDB writes its prompt. Take a look at command_loop() in top.c. However, if you can't get your clear_xgrab (or whatever you called it) program to work, I don't think you'll have any more success via this route. Keep in mind that gdb is not part of the X11 client that you're attempting to debug. That being the case, it shouldn't matter whether your ungrab code is in gdb or in a separate program. (Either it'll work in both places or fail in both places.) Kevin ___ Bug-gdb mailing list [EMAIL PROTECTED] http://mail.gnu.org/mailman/listinfo/bug-gdb
Re: [Bug-gdb] GDB and X11 server grabs
Dixit Kevin Buettner (2000-09-14 16:34): > Also, it's possible to run commands in the shell via the `shell' > command, so the original poster (Pierre) could put something like the > following in his .gdbinit file: > > define hook-stop > shell clear_xgrab > end > > Provided that a suitable external program called `clear_xgrab' was > created, this would do what the original posted wanted. > > (I still think it's better to use two machines to do this type of > debugging though.) I wrote a program that calls XUngrabServer(), but it did not have any effect. I added a call to XGrabServer() juste before, but still without effect. Perhaps a server grab is specific to each X11 client. Ungrabbing from one X11 client would not affect grabs by other clients. I also tried to run Xnest, as Gary Aviv suggested, but it failed this way: failed to set default font path '/usr/X11R6/lib/X11/fonts/misc/,/usr/X11R6/lib/X11/fonts/Speedo/,/usr/X11R6/lib/X11/fonts/Type1/,/usr/X11R6/lib/X11/fonts/75dpi/,/usr/X11R6/lib/X11/fonts/100dpi/' Fatal server error: could not open default font 'fixed' I guess I could make these two solutions work if I hack at them somewhat. However, it would remain unusually complicated to debug an X11 application under GDB. A Windows programmer would be quick to point out that this situation does not happen on his platform. (Although the drop down menu remains displayed over the Visual Studio window...) I would be curious to know how this problem is handled under Windows. I wouldn't mind patching my own copy of GDB to experiment with XUngrabServer(). Could someone tell me what function of the GDB sources I should study to do this? I would like to add some code where GDB writes its prompt. -- Pierre Sarrazin ___ Bug-gdb mailing list [EMAIL PROTECTED] http://mail.gnu.org/mailman/listinfo/bug-gdb
Re: [Bug-gdb] GDB and X11 server grabs
On Sep 14, 6:42pm, Benoit Hudson wrote: > On Thu, Sep 14, 2000 at 01:06:47PM -0700, Kevin Buettner wrote: > > other things too. E.g, it might be okay if you added a hook which says > > to run a user specified shell command every time gdb stops and > > displays a prompt. (I still don't know if such a patch would be > > accepted, but it'd have a much better shot than one which has explicit > > knowledge about the X Window system.) > > Isn't that the 'commands' command? No. The 'commands' command is used to attach some commands to a breakpoint. They won't run the commands when single stepping or gdb stops due to some signal. But I found the following in the gdb manual: In addition, a pseudo-command, `stop' exists. Defining (`hook-stop') makes the associated commands execute every time execution stops in your program: before breakpoint commands are run, displays are printed, or the stack frame is printed. Also, it's possible to run commands in the shell via the `shell' command, so the original poster (Pierre) could put something like the following in his .gdbinit file: define hook-stop shell clear_xgrab end Provided that a suitable external program called `clear_xgrab' was created, this would do what the original posted wanted. (I still think it's better to use two machines to do this type of debugging though.) Kevin ___ Bug-gdb mailing list [EMAIL PROTECTED] http://mail.gnu.org/mailman/listinfo/bug-gdb
Re: [Bug-gdb] GDB and X11 server grabs
On Thu, Sep 14, 2000 at 01:06:47PM -0700, Kevin Buettner wrote: > other things too. E.g, it might be okay if you added a hook which says > to run a user specified shell command every time gdb stops and > displays a prompt. (I still don't know if such a patch would be > accepted, but it'd have a much better shot than one which has explicit > knowledge about the X Window system.) Isn't that the 'commands' command? -- Benoît ___ Bug-gdb mailing list [EMAIL PROTECTED] http://mail.gnu.org/mailman/listinfo/bug-gdb
Re: [Bug-gdb] GDB and X11 server grabs
On Thu, 14 Sep 2000, Pierre Sarrazin wrote: > A GDB breakpoint can totally freeze an X11 display when debugging > a GUI application, if the app makes a "server grab." > > For example, if the application has a pull-down menu and I put > a breakpoint in the menu's callback, then the following happens: > > - the menu is opened and an X11 server grab happens (in order to > catch all mouse events even if they are outside the menu's window); > > - the callback is called and GDB stops on it due to the breakpoint; > > - GDB expects commands from the user, but the user cannot type > anything anywhere in the display because of the server grab; > of course, the menu cannot be closed because the app is stopped. > > One way to get out of this is to login through the network and > kill GDB. Usually, I access the machine through a VNC remote > display. In addition, I telnet into the machine and run GDB in it, > sending the display to the VNC/X11 server. When the breakpoint is > reached, I can still control GDB through the telnet session. > > Is there a better way? I would imagine that GDB could automatically > try to end an X11 server grab every time it displays its prompt. > > -- > Pierre Sarrazin <[EMAIL PROTECTED]> > ___ > Bug-gdb mailing list > [EMAIL PROTECTED] > http://mail.gnu.org/mailman/listinfo/bug-gdb > Yes. Use Xnest which gives you a X server which runs inside your host X server. So the procedure is something like this: Xnest :1 & # from a local xterm, an X server is run in a window as screen 1 twm -display :1 & # run a window manager in Xnest, for example twm, xhost + # to turn off security in Xnest server Now run your application under gdb (or in emacs, etc.) passing the application the additional argument "-display :1". The application will then run in a window under Xnest. If your application does not accept the -display argument you will have to "set env DISPLAY=:1" in gdb prior to running it. Now you can set breakpoints even during pointer grabs because the grab occurs only in the Xnest session. So, you will not get locked up as you describe above. [EMAIL PROTECTED] ___ Bug-gdb mailing list [EMAIL PROTECTED] http://mail.gnu.org/mailman/listinfo/bug-gdb
Re: [Bug-gdb] GDB and X11 server grabs
On Sep 14, 3:32pm, Pierre Sarrazin wrote: > A GDB breakpoint can totally freeze an X11 display when debugging > a GUI application, if the app makes a "server grab." > > For example, if the application has a pull-down menu and I put > a breakpoint in the menu's callback, then the following happens: > > - the menu is opened and an X11 server grab happens (in order to > catch all mouse events even if they are outside the menu's window); > > - the callback is called and GDB stops on it due to the breakpoint; > > - GDB expects commands from the user, but the user cannot type > anything anywhere in the display because of the server grab; > of course, the menu cannot be closed because the app is stopped. > > One way to get out of this is to login through the network and > kill GDB. Usually, I access the machine through a VNC remote > display. In addition, I telnet into the machine and run GDB in it, > sending the display to the VNC/X11 server. When the breakpoint is > reached, I can still control GDB through the telnet session. > > Is there a better way? I would imagine that GDB could automatically > try to end an X11 server grab every time it displays its prompt. The best way to debug the portions of a GUI application that have to interact with the display is to do it from another display. Although it is possible to use Xnest or Xvnc to give the illusion of multiple displays on a single display, in practice, this usually doesn't work out very well since you end up having to move the mouse (thus generating more X events) to give focus back to gdb. This means that you're really better off having two machines, one on which to run the app that you're debugging and the other for displaying your debugger session. It might be possible to hack gdb to release the grab, but IMO this would be a really ugly hack both from the gdb side of the world as well as from the X11 side. If I were the maintainer for the affected part of gdb, I would probably not accept such a patch unless it were in the form of some sort of generic hook that could be used to do other things too. E.g, it might be okay if you added a hook which says to run a user specified shell command every time gdb stops and displays a prompt. (I still don't know if such a patch would be accepted, but it'd have a much better shot than one which has explicit knowledge about the X Window system.) ___ Bug-gdb mailing list [EMAIL PROTECTED] http://mail.gnu.org/mailman/listinfo/bug-gdb
